I've flown in 11F on a relatively long flight (PHX-CUN) and was pretty happy with it. The FA was only in the seat for takeoff and landing so I was able to stretch out for the entire flight.

Usually seat width is my #1 consideration but that's due to shoulder space so the seat itself being narrower due to the tray table didn't bother me (my shoulder space is the same). I'm also not skinny by any stretch of the imagination, but I still fit in the seat just fine.

It's also worth pointing out that the narrowbody airbuses have wider seats than a 737, by about an inch. I find this to be a huge difference (again, it's all about shoulder space for me). I'm not sure how much width the tray table takes away but there still may be more space than someone is used to if they fly a lot of 737s.